This invention relates generally to inflatable restraint systems and, more particularly, to an improved closure for use with an installation of an inflatable cushion, commonly referred to as an air bag.
Safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., "passive restraint systems", and particularly those restraint systems incorporating inflatable bags or cushions, as well as the use of such systems in motor vehicles have been the subjects of much discussion as the desirability of the use of such passive restraint systems has gained general acceptance in the United States.
It is well known to protect a vehicle occupant using a cushion or bag that is inflated/expanded with gas, e.g., an "air bag", when the vehicle encounters sudden deceleration, such as in a collision. During deployment, the rapidly evolving gas with which the bag is typically filled is an inert gas, e.g., nitrogen. In such systems, the cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the air bag system, gas is discharged from an inflator to rapidly inflate the bag. The cushion, upon inflation, serves to restrain the movement of the vehicle occupant as the collision proceeds. In general, such air bags are commonly designed to be inflated in no more than about 30-60 milliseconds.
Inflatable restraint systems have been devised for automotive vehicles in which one or more air bags are stored in one or more storage compartments within the vehicle. In general, an air bag provided for the protection of a vehicle driver, i.e., a driver side air bag, is stored within a housing mounted in a storage compartment located in the steering column of the vehicle. Whereas, an air bag for the protection of a front seat passenger, i.e., a passenger side air bag, is typically stored within a housing mounted in the instrument panel/dash board of the vehicle. In either case, the housing of such an air bag assembly generally has a cover or some form of closure panel member. The closure commonly includes a face portion which, in the standard state, provides closure to the assembly and which, upon activation of the assembly and initial bag deployment, typically forms one or more "doors" which form an opening through which the air bag will be deployed.
In order to reduce the likelihood of tampering with the system, the closure panel member is commonly designed so as to minimize the visual impression of the presence of the air bag and air bag deployment opening thereunder. Thus, such closure panel members are typically designed to match or otherwise be compatible with the interior design of the vehicle.
Also to this end, appearance or otherwise cosmetic problems such as read through and sink marks are sought to be avoided. Read through (e.g., where shapes or features on the backside of the closure can be relatively easily discerned from a viewing of the front side of the closure) and sink marks (e.g., where the closure has an undesired, lower or uneven outer surface) can result from processing. For example, when the closure is prepared by molding fabrication of a thermoplastic material, an uneven shrinkage of the closure material upon processing can result in read through and/or sink marks. Such uneven shrinkage can, for example, occur as a result of the item being processed having relatively widely varying thicknesses and thus varying processing time and condition requirements.
In practice, closure panel members are commonly designed so that the face portion of the closure can be torn or otherwise opened along predetermined lines as a result of the force exerted against the closure by way of the inflating air bag and, thus, form air bag release doors. To this end, the closure is typically pre-weakened, such as by perforating or reducing the thickness of the cover, for example, along such preformed tear lines, paths or seams, generally commonly referred to herein as "tear ways". Furthermore, primarily to facilitate manufacture and operation, the face portion of prior art closures are commonly of uniform thickness except for the tear ways such as described above. Upon formation, the doors commonly remain joined to the closure via one or more hinge sections which permit the doors to move allowing the air bag to deploy through the resulting opening.
The component parts of such closures, fabricated from the thermoplastic rubber SANTOPRENE (a trademark of Monsanto Company), commonly have the following thicknesses:
______________________________________ PART THICKNESS (mm) ______________________________________ Door 2-3 Tear ways 0.4-1.1 Hinge 1.6-3 ______________________________________
As will be appreciated, the air bag deployment process is of necessity a very rapid process and, at least partially as a result thereof, commonly results in the door or doors opening with such force and energy that the closure can tear in an undesired and/or uncontrolled manner, such as tearing outside of the tear way such as into or through the hinge section, joining an air bag deployment door with the assembly.
Such undesired and/or uncontrolled tearing of the closure can result in the air bag closure breaking into or forming separate pieces. For example, should the tearing action proceed through the hinge section joining the door to the balance of the closure and/or assembly, the air bag release door can become detached from the closure or the balance of the system installation. Such a fragment can then act as a projectile capable of damaging or hurting vehicle occupants.
Also, the manner in which a closure is torn can detrimentally affect the manner in which the air bag is inflated and the shape or form taken thereby, and thus result in inflation of the underlying air bag in a non-optimal manner.
Various approaches have been employed in an attempt to overcome the problem of such undesired tearing. Unfortunately, many of the approaches for minimizing undesired closure tearing are so burdensome as to limit the flexibility and freedom in the designing of closures for specific installations.
In one approach, a closure member made of plastic is strengthened or reinforced by embedding therein a secondary material such as a section of a highly tear resistant material. For example, U.S. Pat. Nos. 4,334,699 and 4,752,083 teach embedding a tear resistant band or a reinforcing element, respectively, in a rupturable cover. An alternative approach has been to vary or alter the shape, size, or dimensions of the tear ways in the closure. For example, U.S. Pat. No. 5,013,065 discloses the use of a rupturable cover having break lines of continuously increasing thickness. U.S. Pat. No. 3,622,176 discloses using V-shaped grooves along the fracture lines and hinge elements having rounded root grooves, so as to avoid fracture. U.S. Pat. No. 5,060,971 discloses using a cover whose thickness is specifically varied along the tear seam. Another example of such an approach is the use of a closure wherein the thickness of the tear ways is gradually increased as the longitudinal end of the tear way is approached.
Other or similar cover groove geometries are shown in other patents including U.S. Pat. Nos. 4,964,652; 5,002,307; 5,069,477; 5,087,071; and 5,143,401.
In addition, tear ways with graduated or steadily varying thickness have been used in an attempt to provide a more controlled tearing of the closure. While the utilization of designs having such tear ways of varying thickness typically may provide greater control over the closure opening process including the site of the initial opening, such designs generally increase the likelihood of certain undesirable forms of closure tearing, such as tearing outside of the tear way. For example, when a closure is undergoing tearing along a tear way and the tearing action reaches a point in the tear way at which there is an abrupt increase in the thickness of the tear way, the abrupt change in thickness can result in tearing outside of the tear way. In the case of a tear way of gradually increasing thickness, as the thickness of the tear way increases, the difference in thickness of material at the tear way and the adjacent sections of the face portion diminishes, increasing the likelihood of non-tear way tearing of the closure.